1. Field of the Invention
The field of the invention is directed to Light Emitting Diode (LED) lighting/illumination systems/fixtures or luminaires. More specifically, the present embodiments are directed to LED lighting systems with phosphor, photo luminescent, wavelength conversion to generate a desired color of light.
2. Description of the Related Art
The introduction of solid state semiconductor devices such as semiconductor light emitting diodes (LEDs) has allowed a new generation of energy efficient lighting systems to come into existence. Today, most lighting fixture designs utilizing LEDs comprise systems in which an LED (or an LED array) replaces conventional system components such as incandescent bulbs, mercury vapor and compact fluorescent lamps. LEDs often further include a phosphor, photo luminescent material, whose light, emitted in response to excitation radiation from the LED in the system, combines with light from the LED to produce the lighting system's illumination product. It is common in such conventional systems to incorporate further elements such as a light reflection backplane, a light diffusing front plane, and color filter pigments and paints.
U.S. Pat. No. 6,350,041 teaches a solid state lamp based on an LED which emits radially dispersed light for room illumination and other applications. The lamp comprises a solid state light source such as an LED or laser which transmits light through a separator to a disperser that disperses the light in a desired pattern and/or changes the color of light. In one embodiment, the light source comprises a blue emitting LED, the separator is a light pipe or fiber optic device and the disperser disperses the light radially and converts some of the blue light to yellow to produce a white light illumination product. The separator spaces the LED a sufficient distance from the disperser such that heat from the LED will not transfer to the disperser when the LED is carrying elevated currents as is necessary for room illumination. Such a lamp provides a solid state light source that can disperse light in many patterns, but is particularly applicable to a radial dispersion of white light for room illumination enabling the lamp to be used as an alternative light source in existing luminaires and lighting fixtures.
While such lighting system designs may have demonstrated properties that are acceptable to some customers, properties such as intensity, color temperature and color perception, for instance, they lack flexibility in how the design components may be placed in the system. Phosphor layers are typically placed, for example, adjacent or in close approximation to a light emitting surface of the LED die/chip from whom they derive their excitation energy. Often, the phosphor layer must be coated directly onto the LED die to achieve the desired intensity and color of the illumination being generated.
A need exists therefore for an improved illumination/lighting system based entirely on solid-state components, as before, but enhanced by providing greater flexibility in the placement of the components in the system.